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| Micro Controllers Discuss all aspects of micro controllers - building them, coding them, etc. All controllers are welcome - PIC, BASIC, Z8 Encore!, etc. |
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11th December 2007, 02:48 PM
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 drive circuit for IR sensor hey i am working on a project and i need to connect at89c51 interrupt to an ir sensor my ir sensor has an output of 2 v, when its nc when its broken, its output goes to .8v i cannot drive my controller with 2v, so made a drive circuit i havent yet connected it to my controller here is the schematic...tell me...is it enuff to convert 2v to 5 v?? thanks Last edited by baftab; 11th December 2007 at 02:53 PM. | |
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11th December 2007, 03:03 PM
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| hi, As the signal Vmax is only 2.1V and the Vbe junction of the transistor is about 0.7V, this means the 10K series resistor has only 1.4V across it. This gives a base current of only 0.14mA!, if the transistor has a gain of 100,the transistor will only have a collector current in the order of 14mA, which is too low to drive a relay. I would reduce the 10K resistor to a value of about 330R. What is the purpose of the relay in the IR sensor circuit, [do not connect as relay to a MCU as you have drawn it, the back emf could damage the MCU] It would be possible to connect a 4K7 resistor in place of the relay and use the transistor collector out of 0V/+5V to drive the MCU pin. [the signal would be inverted, but this should be easy to correct in the program].
__________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/ Last edited by ericgibbs; 11th December 2007 at 03:08 PM. | |
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11th December 2007, 04:07 PM
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| oh am sorry...i am not connecting a relay... i was thinking of directly connecting the output to the mcu....the two wires tht say "to microcontroller" i dont intend to drive a relay...wrote it wrongly in the title... i'll change the base resistor , but the collector resistor is fine..right?? i dont intend to use a relay is there anything else wrong?? | |
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11th December 2007, 04:11 PM
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The collector resistor is OK. I see from your drawing that you have +6V to the top of the resistor, will your MCU accept a +6V input! or does it specify a maximum of +5V?
__________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/ | ||
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11th December 2007, 04:20 PM
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| hi, The 10K will limit the input to the MCU pin to +5V.
__________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/ Last edited by ericgibbs; 7th July 2008 at 12:22 PM. | |
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11th December 2007, 05:04 PM
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| thanks a lot  | |
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12th December 2007, 10:49 PM
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| one thing more using uln2803...will it work? i mean instead of a frive circuit...can i use uln2803??? | |
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29th January 2008, 12:14 PM
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| dear sir, can u send me remote controller circuit for control two relayas !! please reply me soon as possible (kasungayantha@yahoo.com) thankyou !! | |
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